U.S. patent application number 13/550699 was filed with the patent office on 2014-01-23 for method and apparatus for adaptively controlling wind park turbines.
The applicant listed for this patent is Hongtao Ma, Robert J. Nelson. Invention is credited to Hongtao Ma, Robert J. Nelson.
Application Number | 20140021720 13/550699 |
Document ID | / |
Family ID | 48626260 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140021720 |
Kind Code |
A1 |
Nelson; Robert J. ; et
al. |
January 23, 2014 |
METHOD AND APPARATUS FOR ADAPTIVELY CONTROLLING WIND PARK
TURBINES
Abstract
A wind turbine park (242) connected to a transmission system
(234). The wind turbine park includes a component (230) for
determining a short circuit ratio and based thereon for determining
a parameter adjustment recipe, and a controller (238) for
controlling an output of the wind turbine park, the controller
(238) executing a control algorithm using a determined parameter
adjustment recipe, the determined parameter adjustment recipe
responsive to the short circuit ratio and determined within the
component (230) or within the controller (238).
Inventors: |
Nelson; Robert J.; (Orlando,
FL) ; Ma; Hongtao; (Orlando, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nelson; Robert J.
Ma; Hongtao |
Orlando
Orlando |
FL
FL |
US
US |
|
|
Family ID: |
48626260 |
Appl. No.: |
13/550699 |
Filed: |
July 17, 2012 |
Current U.S.
Class: |
290/44 |
Current CPC
Class: |
H02J 2300/28 20200101;
Y02E 10/763 20130101; Y02E 40/34 20130101; H02J 3/16 20130101; Y02E
40/30 20130101; Y02E 10/76 20130101; H02P 9/007 20130101; G06F
19/00 20130101; H02J 3/38 20130101; H02J 3/386 20130101; H03H 1/00
20130101; H02J 3/381 20130101 |
Class at
Publication: |
290/44 |
International
Class: |
H02P 9/04 20060101
H02P009/04 |
Claims
1. A wind turbine park connected to a transmission system, the wind
turbine park comprising: a component for determining a short
circuit ratio and based thereon for determining a parameter
adjustment recipe; and a controller for controlling an output of
the wind turbine park, the controller executing a control algorithm
using a determined parameter adjustment recipe, the determined
parameter adjustment recipe responsive to the short circuit ratio
and determined within the component or within the controller.
2. The wind turbine park of claim 1 wherein the component
determines the short circuit ratio according to one of a
predetermined schedule, periodically, randomly and whenever a
significant change occurs in system components.
3. The wind turbine park of claim 2 wherein a significant change in
system components comprises one of a generator outage, a
transmission line outage, a generator placed back into service and
a line placed back into service.
4. The wind turbine park of claim 1 wherein the component
determines the short circuit ratio from an equation SCR=MVAsc/MWt
where MVAsc is a product of the transmission system three-phase
short circuit current, the pre-fault line voltage, and the square
root of 3, with that quantity divided by 1E6, and MWt is the
aggregate turbine MWt of the wind turbine park.
5. The wind turbine park of claim 4 wherein the component
determines MVAsc by injecting reactive power into the transmission
system or absorbing reactive power from the transmission system,
measuring a resulting voltage change, and determining MVAsc from an
equation .DELTA.V/V=.DELTA.Q/MVAsc, where V is a system voltage
before the step of injecting or absorbing is executed, .DELTA.V is
a change in the system voltage due to reactive power injection or
absorption and .DELTA.Q is a quantity of reactive power injected or
absorbed.
6. The wind turbine park of claim 5 wherein the component injects
reactive power into the transmission system by switching a
capacitor into the transmission system or by switching a reactor
out of the transmission system.
7. The wind turbine park of claim 5 wherein the component absorbs
reactive power from the transmission system by switching a
capacitor out of the transmission system or by switching a reactor
into the transmission system.
8. The wind turbine park of claim 1 wherein the parameter
adjustment recipe comprises one or more of a proportional gain
value, an integral gain value and a ramp-up rate value.
9. The wind turbine park of claim 1 wherein the component
determines the short circuit ratio based on a determined
transmission system reactance-to-resistance ratio (X/R).
10. The wind turbine park of claim 1 wherein the component
determines the short circuit ratio based on synchrophasor
information.
11. The wind turbine park of claim 1 wherein the wind turbine park
comprises a plurality of sub-parks connected via overhead
transmission lines, and wherein the method is executed
independently for each sub-park.
12. A method for adaptively controlling a wind turbine park
according to a determined short circuit strength of a transmission
system to which the wind turbine park supplies power, wherein one
or more parameter adjustment recipes for use in a wind turbine park
control algorithm are available, the method comprising: determining
a system short circuit ratio; selecting a recipe from the parameter
adjustment recipes responsive to the system short circuit ratio;
and controlling the output of the wind turbine park according to
the control algorithm and the selected parameter adjustment
recipes.
13. The method of claim 12 wherein a step of determining is
executed according to one of a predetermined schedule,
periodically, randomly and whenever a significant change occurs in
system components.
14. The method of claim 12 wherein the step of determining
comprises determining the system short circuit ratio from an
equation SCR=MVAsc/MWt where MVAsc is a product of the transmission
system three-phase short circuit current, the pre-fault line
voltage, and the square root of 3, with that quantity divided by
1E6, and MWt is the aggregate turbine MWt of the wind turbine
park.
15. The method of claim 14 further comprising: injecting reactive
power into the transmission system or absorbing reactive power from
the transmission system; measuring a resulting voltage change; and
determining a term MVAsc from V/V=.DELTA.Q/MVAsc, where V is a
system voltage before the step of injecting or absorbing is
executed, .DELTA.V is a change in the system voltage due to
reactive power injection or absorption and .DELTA.Q is a quantity
of reactive power injected or absorbed.
16. The method of claim 14 wherein injecting reactive power into
the transmission system comprises switching a capacitor into the
transmission system or switching a reactor out of the transmission
system, and wherein absorbing reactive power from the transmission
system comprises switching a capacitor out of the transmission
system or switching a reactor into the transmission system.
17. The method of claim 12 wherein the one or more parameter
adjustment recipes comprise one or more of a proportional gain, an
integral gain and a ramp-up rate.
18. The method of claim 12 wherein a step of determining further
comprises determining the system short circuit ratio based on one
of a system reactance to resistance ratio (X/R) and synchrophasor
information.
19. The method of claim 12 wherein the wind turbine park comprises
a plurality of sub-parks connected via overhead transmission lines,
and wherein the method is executed independently for each sub-park.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to a method and apparatus
for controlling operation of a wind park, and more specifically to
adaptively controlling the wind park responsive to the conditions
of the grid to which the wind turbine park is connected.
BACKGROUND OF THE INVENTION
[0002] Due to current efforts to reduce consumption of natural
resources, the conversion of wind energy to electrical energy using
wind turbine generators is becoming more prevalent. Wind turbines
exploit wind energy by converting the wind energy to electricity
for distribution to end users.
[0003] A fixed-speed wind turbine is typically connected to the
grid through an induction (asynchronous) generator for generating
real power. Wind-driven blades drive a rotor of a fixed-speed wind
turbine that in turn operates through a gear box (i.e., a
transmission) with a fixed rotational speed output. The fixed-speed
gear box output is connected to an induction generator for
generating real power.
[0004] The rotor and its conductors rotate faster than the rotating
flux applied to the stator from the grid (i.e., higher than the
synchronous field frequency). At this higher speed, the direction
of the rotor current is reversed, in turn reversing the counter EMF
generated in the rotor windings, and by generator action
(induction) causing current (and real power) to be generated in and
flow from the stator windings.
[0005] The frequency of the generated stator voltage is the same as
the frequency of the applied stator voltage providing the
excitation. The induction generator may use a capacitor bank for
reducing reactive power consumption (i.e., the power required to
generate the stator flux) from the power system.
[0006] The fixed-speed wind turbine is simple, reliable, low-cost
and proven. But its disadvantages include uncontrollable reactive
power consumption (as required to generate the stator rotating
flux), mechanical stresses, limited control of power quality and
relatively inefficient operation. In fact, wind speed fluctuations
result in mechanical torque fluctuations that then result in
fluctuations in the electrical power on the grid.
[0007] In contrast to a fixed-speed wind turbine, the rotational
speed of a variable speed wind turbine can continuously adapt to
the wind speed, with the blade speed maintained at a relatively
constant value corresponding to a maximum electrical power output
through the use of a gear box disposed between the wind turbine
rotor and the generator rotor.
[0008] The variable speed wind turbine may be of a doubly-fed
induction generator (DFIG) design or a full converter design. The
doubly-fed induction generator uses a partial converter to
interchange power between the wound induction generator rotor and
the power system. The full converter wind turbine is typically
equipped with a synchronous or asynchronous generator (the output
of which is a variable frequency AC based on the wind speed) and
connected to the grid through a power converter that rectifies the
incoming variable-frequency AC to DC and inverts the DC to a
fixed-frequency 60 Hz AC. Variable-speed wind turbines have become
widespread due to their increased efficiency over fixed-speed wind
turbines and superior ancillary service capabilities.
[0009] FIG.1 illustrates components of an exemplary variable speed
wind turbine 8, including rotor blades 12 for converting wind
energy to rotational energy for driving a shaft 16 connected to a
gearbox 18. The wind turbine also includes a structural support
component, such as a tower and a rotor pointing mechanism, not
shown in FIG.1. The gearbox 18 converts low speed rotation to high
speed rotation, as required for driving a generator 20 to generate
electricity.
[0010] Electricity generated by the generator 20 is supplied to a
power electronics system 24 to adjust the generator output voltage
and/or frequency for supply to a grid 28 via a step-up transformer
30. The low-voltage side of the transformer is connected to the
power electronics system 24 and the high-voltage side to the grid
28. Generally, the power electronics system imparts characteristics
to the generated electricity that are required to match electricity
flowing on the grid, including controllable active power flow and
voltage regulation and improved network voltage stability.
[0011] One embodiment of the power electronics system 24 includes a
generator-side converter for converting the generated AC
electricity to DC and an output capacitor for filtering the DC
current. DC current is supplied to a line side converter (inverter)
for producing 60 Hz AC power supplied to the grid 28. The amount of
power available from the wind turbine is determined by operation of
the generator-side converter.
[0012] One type of converter employed in a variable speed wind
turbine, referred to as a full converter or a back-to-back
converter, comprises a power converter connected to the generator
side, a DC link and a power converter connected to the grid. The
full converter converts an input voltage, i.e., a fixed frequency
alternating current, a variable frequency alternating current (due
to the variable wind speed) or a direct current, as generated by
the wind turbine, to a desired output frequency and voltage as
determined by the grid that it supplies. Typically using
thryistors, the full converter converts the electricity produced by
the generator to DC and transfers this energy to the DC link.
[0013] From the DC link the electricity is supplied to the
grid-side active converter where it is transformed to fixed
frequency AC electricity and supplied to the grid.
[0014] FIG.2 illustrates a wind park or wind farm 50 comprising a
plurality of wind turbines 54 (such as the variable speed wind
turbine 8 illustrated in FIG.1 or a fixed speed wind turbine)
connected through a feeder or collector 56, which serves as a
distribution system within the wind turbine park. Several feeders
may be required for an average size wind turbine park.
[0015] The wind park 50 further comprises a wind park controller 60
and a wind park transformer 64. The wind park controller 60
controls operation of the wind turbines 54. The transformer 64
connects the wind park collector 56 to a utility system or grid 68
via a point of common coupling (PCC) 72.
[0016] The wind turbines 54 bidirectionally communicate with the
controller 60 via control lines 78. The signals carried over the
control lines 78 relate to wind turbine output power, wind turbine
status, a reference power, wind turbine operational commands, etc.
The controller 60 is also connected to the PCC 72 via a control
line 80. This connection allows the controller 60 to detect power
parameters, such as voltage and current, at the PCC 72.
[0017] The wind park controller 60 generally fulfills a plurality
of control functions related to the individual wind turbines 54 and
therefore the output of the wind park 50. For example, the wind
park controller 60 collects data characterizing the current state
of each wind turbine 54 and in response thereto independently
controls operation of each wind turbine 54.
[0018] The wind park 50 is only an example of a conventional wind
turbine park. The teachings of the present are not restricted to
the depicted layout of FIG.2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention is explained in the following description in
view of the drawings that show:
[0020] FIG. 1 is a block diagram of a prior art wind turbine.
[0021] FIG. 2 is a block diagram of a prior art wind turbine
park.
[0022] FIG. 3 is a flow chart depicting one embodiment of method
steps associated with the present invention.
[0023] FIG. 4 is a block diagram of a system for controlling a wind
turbine park.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention discloses the use of an adaptive
control algorithm for controlling a power system, where the
algorithm is modified in response to changes in a measured local
voltage when reactive power is injected into the system to increase
the system voltage or absorbed from the system to decrease the
system voltage. The amount by which the local voltage changes as a
result of a change in VAR generation or absorption is an indication
of the system impedance and also allows calculation of the short
circuit ratio (SCR), as more completely described below.
[0025] Short circuit "strength" is a measure of the ability of the
system to maintain a system voltage within predefined limits when a
short circuit occurs on the system. A system designated as a
"strong" system typically has a short circuit ratio of about 10 or
higher. The short circuit ratio (SCR) is the ratio of the
three-phase short circuit MVA as delivered during a short circuit
event divided by the nominal turbine MWt capacity (megawatt
thermal, i.e., the heat generating capacity of the steam-producing
plant supplying the steam to turn the turbine).
[0026] In effect, the short circuit ratio is a convenient indicator
of the system impedance. It is relatively easy to determine the
short circuit ratio (also referred to as short circuit MVA) at any
point on the transmission system under system design conditions
(e.g., all generators in service and all lines "in"). However when
lines and/or generators are taken out of service during normal
operation of the system, the actual short circuit ratio may be
considerably lower than its design value. Without knowledge of the
short circuit ratio under such normal operating conditions, control
of the system voltage is difficult.
[0027] The short circuit MVA is the short circuit current
(kAmps/phase) multiplied by the pre-fault line-to-ground voltage
(kV) times three (for a three phase system). The resulting product
is simply a measure of the impedance of the transmission system. A
high impedance system has a low short circuit MVA. Note that the
short circuit MVA is not related to the wind turbines, and in fact
is calculated with the wind turbines disconnected from the
system.
[0028] The SCR is also an indication of the system's ability to
respond to reactive power injections and absorptions. A low-SCR
("weak") system is very responsive to reactive power injections (or
absorptions) i.e., the system voltage changes rapidly as the amount
of reactive power injected (or absorbed) changes. It is therefore
difficult to stabilize the system voltage on a weak system. A
high-SCR ("strong") system is largely unresponsive to reactive
power injections (and absorptions) and the system voltage is
therefore more easily and more rapidly controlled. A "strong"
system is therefore considered more robust.
[0029] In equation form, the SCR is,
SCR=MVAsc/MWt (1)
where:
[0030] MVAsc is a product of the transmission system three-phase
short circuit current (amperes), the pre-fault line nominal voltage
(volts, line-to-line), and the square root of 3 (equals 1.732),
with that quantity divided by 1E6, and
[0031] MWt is the aggregate turbine capability MWt (i.e., a sum of
the megawatts of wind turbine capability within the wind turbine
park) at the location where the wind turbine park bus is connected
to the grid or transmission system. A wind turbine has a maximum
capability, i.e., a 2.3 MW turbine can generate 2.3 MW at its rated
wind speed (and higher), less at lower wind speeds. Therefore a
wind park with 44 turbines, each rated at 2.3 MW, would have a MWt
value of 101.2 (that is, 2.3.times.44=101.2).
[0032] Generally, a system operator identifies segments of the
system as either "weak" or "strong" by defining SCR values
associated with each of these two classifications. There is no
industry-wide uniform definition for "weak" and "strong" classes.
Since most wind turbine parks are located where the prevailing wind
conditions are best and such sites are typically a significant
distance from load centers, many wind turbine parks are classified
as having "weak" short circuit strength.
[0033] Prior art wind park control systems typically assume some
nominal level of system short circuit strength (i.e., for a
proximate region of the grid to which the park is connected) and
employ a control algorithm (and its constituent parameter values)
based on that static assumption. The control algorithm is used for
controlling system voltage. Such a static setting requires use of
control algorithm parameters that are based on the lowest SCR value
that is likely to occur during the design life of the park. But
such a static setting penalizes performance of the wind turbine
park because it applies the same control algorithm for all values
of actual SCR. For example, applying a control algorithm that
exhibits a slow response, which is customary for use with weak
systems, to a system that exhibits a stronger short circuit
strength protracts the system recovery time. In certain
applications this protracted recovery time may be detrimental to
the system.
[0034] The principal intent of the present invention is to regulate
the system voltage during steady state conditions (i.e., normal;
system operation) and during faults. Although system response
during faults is important, regulation during faults is of less
importance only because the faults occur infrequently.
[0035] A weak system generally requires a slow response to control
the system voltage or a fast response with supplemental
stabilization controls can be employed. During steady state
operation of a very weak system, the opening or closing of a
relatively small circuit breaker may cause voltage oscillations or
flicker. A strong system permits a fast response without the need
for supplemental stabilization controls. In any case, the present
invention determines the short circuit strength and executes the
appropriate control algorithm to control the system voltage.
[0036] Determining the short circuit strength of the system is
important the use of a control system developed for a so-called
"strong" power system may create oscillatory behavior when applied
to a weak system. Conversely, the use of a weak system control
algorithm typically provides a sluggish response when applied to
strong systems. Adapting the control algorithm to the system's
short circuit strength provides more effective system control
following the occurrence of a short circuit.
[0037] To avoid use of a static control algorithm and thus avoid
employing a less than optimum control algorithm, the present
invention determines a short circuit strength for a proximate
region of the grid (based on a determined short circuit ratio) and
adjusts the control algorithm parameters accordingly to optimize
the response time based on the then-prevailing system conditions.
The short circuit strength can be determined periodically,
randomly, on a schedule determined by the system operator or when a
substantial system equipment change is made. Thus the present
invention provides a dynamic or adaptive system response based on
recently determined short circuit strength values. Advantageously,
it is therefore not necessary to impose a static short circuit
strength assumption.
[0038] Siemens, the assignee of the present invention, prefers to
have a short circuit ratio of at least five when wind turbines are
connected to the grid.
[0039] When the grid exhibits an SCR of less than about five, some
adjustments to the wind turbine park control algorithm are
preferred to accommodate the poor voltage regulation associated
with this grid. For an SCR of about three or less it is necessary
to use so-called "weak-grid" control algorithms, which purposefully
slow the rate of active power recovery (i.e., voltage) following a
fault.
[0040] More generally, when a numerical value or qualitative
classification of the short circuit strength has been determined
for the local grid, based on the numerical value obtained from the
SCR equation above, then according to the present invention the
control algorithm for the wind turbine park is adjusted responsive
to that numerical value or qualitative classification. Further,
each time the numerical value or qualitative classification has
been determined, the control algorithm for the wind turbine park is
modified (e.g., certain parameters associated with the control
algorithm are adjusted).
[0041] The following methodology is employed to determine an SCR
value. It is known that a step reactive power injection of
.DELTA.Q, in a system with a short circuit MVA of MVAsc, causes a
voltage change of .DELTA.V in accordance with
.DELTA.V/V=.DELTA.Q/MVAsc (2)
where:
[0042] V is a system voltage before the reactive power injection or
absorption,
[0043] .DELTA.V is a change in the system voltage due to the
reactive power injection and
[0044] .DELTA.Q is the reactive power injection. V and .DELTA.V are
per unit voltage quantities.
[0045] For example, if the MVAsc value is 1000 MVA, and V is 1 per
unit (100%), an injection of 20 MVA (reactive power) increases the
voltage by about 2%. If MVAsc is 500 MVA, the same injection causes
a 4% change in the system voltage.
[0046] By using equation (2) above, the present invention
determines the MVAsc by determining the system voltage (V) before
the reactive power injection (or absorption), injecting (or
absorbing) a known amount of reactive power (.DELTA.Q) into the
system, and measuring the resulting system voltage change
(.DELTA.V). Equation (1) above is then used to determine the SCR,
i.e., by dividing the MVAsc value by a sum of the "local" turbine
MW thermal ratings. The amount by which the voltage changes
(.DELTA.V) indicates the system's short circuit strength.
[0047] Thus one can use this methodology to estimate the short
circuit strength of the system with reasonable accuracy. The effect
will be particularly prevalent, and easily observed, for the low
short circuit strength values (a "weak" system) normally
encountered near wind facilities.
[0048] Although this analysis is simplified in that if the
injection of reactive power is provided by turbines the turbine
terminal voltage also changes, this complexity can be easily
considered in a more detailed analysis.
[0049] In lieu of changing the turbine terminal voltage, the
reactive power injected into (or absorbed from) the system can also
be obtained by switching capacitors or reactors into or out from
the power system.
[0050] Changing the reactive power injected into or absorbed from
the grid (e.g., stepping it up or down) to determine MVAsc and then
employing equation (1) to determine the SCR, according to the
present invention, offers a convenient technique to estimate the
short circuit strength of a system.
[0051] In one embodiment, after changing the reactive power the
system voltage is measured at the wind turbine park terminals,
i.e., where the wind park is connected to the grid (the PCC 72 of
FIG. 2). This measurement can be made at either the high voltage
side or the low voltage side of the transformer that connects the
park to the grid. The voltage can also be measured at the output
terminals of the wind turbines. Preferably the voltage is measured
at the turbine terminals. The amount of reactive power change and
the resulting line voltage change is used to determine the short
circuit strength of the system as explained above.
[0052] In many systems, the normal SCR value may be high and
therefore indicative of a strong system. But the value may fall by
about an order of magnitude when a line outage or a generator
outage (in particular a proximate generator) occurs. Such a change
in the operative system components and its effect on the SCR must
therefore be considered in selecting appropriate parameters for the
wind turbine park control algorithm. Thus according to the present
invention, whenever there is a significant change in the system
components the SCR value should be determined and the appropriate
parameters for the wind turbine park control algorithm
selected.
[0053] This determined SCR can then be used to dynamically (and at
various times as desired) adjust gains, time delays, and other
parameters of the control algorithm to optimize performance of the
voltage regulation system and the power controls of the wind
park.
[0054] Preferably the control algorithm parameters to be adjusted
comprise the proportional and integral gains, both at the turbine
and at the wind park. These algorithms comprise adjustments in the
gains and power recovery rates. Also, the ramp-up rate (time
constant) of real power following a low-voltage incident can be
adjusted.
[0055] Preferably, the parameters to be adjusted and the amount of
parameter adjustment for different system strength levels can be
predetermined then put into operation as required based on the
determined system strength. This technique is a significant
improvement over the prior art methodology that uses one set of
algorithm parameters for all systems and for all SCR values.
[0056] The parameters to be adjusted and the amount of parameter
adjustment (or a new parameter value) are referred to as a
parameter adjustment recipe. Each recipe may contain a value for
one or more of the parameters used in the wind turbine park control
algorithm. For example a first recipe may contain a value for a
first parameter used in the algorithm, and a second recipe may
contain a value for the first and also a second parameter in the
algorithm.
[0057] For example, for a very weak system the gains are adjusted
appropriately, but the adjustment is generally accomplished on a
site-by-site basis. For a system with an SCR value of between about
2 and 3 the parameter adjustment recipe may suggest setting Kp
(proportional gain) to about 2, Ki (integral gain) to about 0.3,
and power ramp rate to 5% per minute). If the SCR falls below 2 a
different parameter adjustment recipe is used for changing the
control algorithm parameters. In a weak system, it is generally
important to refrain from generating too much real power
immediately after a low voltage condition, so reactive power is
used to stabilize the system voltage, i.e., prevent the system
voltage from oscillating excessively.
[0058] In a strong system full power production can begin
immediately after the low voltage condition disappears.
[0059] This invention provides an inexpensive but useful
improvement in control performance, particularly in situations
where a weak grid control is used because of the possibility, which
in practice seldom occurs, of a line or generator outage.
[0060] FIG. 3 illustrates a block diagram associated with the
present invention for adaptively controlling a wind turbine park.
At a step 200 a plurality of parameter adjustment recipes for use
in the wind turbine park control algorithm for controlling an
output of the wind turbine park are identified. At a step 204 a
system short circuit ratio is determined. At a step 208 a parameter
adjustment recipe is selected from among the plurality of parameter
adjustment recipes responsive to the determined short circuit
ratio. At a step 212 the output of the wind turbine park is
controlled according to the selected parameter control recipe as
used in the wind turbine park control algorithm.
[0061] With reference to FIG.2, the control algorithm for
controlling the wind turbine park output resides in the controller
60 or within one or more of the wind turbines 54.
[0062] A block diagram of FIG. 4 depicts a depicts a component 230
for determining an SCR value of a transmission system 234 as
described above. The component supplies the determined SCR value to
a controller 238. A parameter adjustment ratio is selected either
in the component 230 or in the controller 238. In either case the
parameter adjustment ratio is responsive to the determined SCR
value and is applied to the control algorithm executed in the
controller 238 to control the output of a wind park 242.
[0063] In another embodiment the parameter adjustment recipes are
selected according to a predetermined range of SCR values. For
example, a first parameter adjustment recipe is used for an SCR
value between 2 and 3 and a second parameter adjustment recipe is
used for an SCR value between 3 and 4. Those ranges can be selected
(e.g., wide ranges or narrow ranges) according to the degree of
granularity desired in selecting a parameter adjustment recipe and
the algorithm parameters embodied in that recipe.
[0064] According to yet another embodiment, synchrophasor
information is used to assess the system short circuit strength.
This information is used to dynamically update the short circuit
strength, based on which control algorithm parameters are selected,
without the need to periodically inject reactive power into the
transmission system or grid.
[0065] In the wind turbine park 50 of FIG. 2, the feeder or
collector 56 typically comprises an underground cable and thus the
system impedance is approximately the same for all wind turbines 56
in the turbine park 50. Therefore the same parameter adjustment
recipe is implemented for each wind turbine 54.
[0066] In some installations the wind farm comprises several
sub-parks that are connected via overhead lines. In this
configuration it may be desirable to use different parameter
adjustment recipes for each sub-park as all will see a different
system impedance.
[0067] According to yet another embodiment, the ratio of system
reactance to resistance (X/R) is determined by measuring a timed
response of the system. Systems with a low X/R ratio are typically
low voltage systems with a low SCR. The X/R ratio can be another
useful parameter to use in optimizing gain values in the various
parameter adjustment ratios for use in the wind turbine park
control algorithm. A system with a high X/R ratio (a high
reactance-to-resistance ratio) has a longer response time than one
with a low X/R ratio. Although this ratio is typically a secondary
consideration in selecting control algorithm parameters, it can be
used to further fine tune the algorithm parameters.
[0068] Although the invention has been shown and described with
respect to a certain preferred embodiments, it is obvious that
equivalent alterations and modifications will occur to others
skilled in the art upon the reading and understanding this
specification and the annexed drawing. In particular regard to the
various functions performed by the above described components
(assemblies, devices, circuits, etc.), the terms used to describe
such components are intended to correspond, unless otherwise
indicated, to any component that performs the specified function of
the described component (i.e., that is functionally equivalent),
even though not structurally equivalent to the disclosed structure
that performs the function in the illustrated exemplary embodiments
of the invention. In addition, while a particular feature of the
invention may have been disclosed with respect to only one of
several embodiments, such feature may be combined with one or more
other features of the other embodiments as may be desired and
advantageous for any given or particular application.
[0069] While various embodiments of the present invention have been
shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions may be made without departing
from the invention herein. Accordingly, it is intended that the
invention be limited only by the spirit and scope of the appended
claims.
* * * * *